Fluoropolymers and, in particular, vinylidene fluoride polymers are used in a wide variety of applications including electrochemical applications.
For instance, fluoropolymers are advantageously used as raw materials in the manufacture of polymer membranes suitable for use in electrochemical devices such as secondary batteries because of their chemical and thermal aging resistance.
Alkaline or alkaline-earth secondary batteries are typically formed by assembling a positive electrode (cathode), a ion conducting membrane and a negative electrode (anode). The ion conducting membrane, often referred to as separator, plays a crucial role in the battery as it must provide for a high ionic conductivity while ensuring effective separation between the opposite electrodes.
Basically, two types of separators can be used: either porous ones, wherein a solution of an electrolyte in a suitable solvent fills the porosity of the separator, or non-porous ones, which are generally either pure solid polymer electrolytes (i.e. electrolytes dissolved in a high molecular weight polyether host, like PEO and PPO, which acts as solid solvent) or gelled polymer electrolyte systems, which incorporate into a polymer matrix a plasticizer or solvent capable of forming a stable gel within the polymer host matrix and an electrolyte.
Nevertheless, gelled polymer electrolytes might not incorporate and retain the liquid plasticizer/electrolyte solution in an effective manner during both manufacturing of the battery and operation of the same, and/or might not possess suitable mechanical properties as required for effective separation of the electrodes.
On the other side, hybridization of organic and inorganic compounds is an important and evolutionary way to create polymeric compounds having, notably, enhanced mechanical properties. To elaborate such organic-inorganic polymer hybrids, sol-gel processes using metal alkoxides is the most useful and important approach. By properly controlling the reaction conditions of hydrolysis and condensation of metal alkoxydes, in particular of alkoxysilanes (e.g. tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS)), in the presence of pre-formed organic polymers, it is possible to obtain hybrids with improved properties compared to the original compounds.
Within this scenario, WO 2011/121078 (SOLVAY SOLEXIS S.P.A.) 10 Jun. 2011 discloses certain fluoropolymer-based hybrid organic/inorganic composites wherein covalent bonds connect fluoropolymer chains to the inorganic domains, said composites being obtained by a process involving the reaction of certain functional fluoropolymers having hydroxyl groups with certain hydrolysable compounds of Si, Ti or Zr, and subsequent hydrolysis and polycondensation of said compounds.
This patent document also mentions that the so obtained hybrid organic/inorganic composites can be notably used for the manufacture of membranes for electrochemical applications and more particularly as separators for Lithium ion batteries.